Coated peroxygen compounds with controlled release, a process for their preparation and their use

ABSTRACT

The invention relates to coated peroxygen compounds, in particular coated sodium percarbonate particles, with a delayed release of the active oxygen (=increased dissolving time). Particles according to the invention comprise an innermost shell layer, comprising at least one hydrate-forming inorganic salt, and an outer shell layer, comprising 0.2 to 3 wt. % alkali metal silicate with a modulus of greater than 2.5, in particular 3 to 5, the outer layer having been prepared using an alkali metal silicate solution with an alkali metal silicate concentration in the range from 2 to 20 wt. %. By lowering the alkali metal silicate concentration in the solution to be used, the dissolving time can be increased for the same shell amount. The dissolving time can be increased greatly by the layer sequence and the concentration of the solution, at a low amount of alkali metal silicate.

The invention relates to coated peroxygen compounds, in particularcoated sodium percarbonate particles, with at least two shell layers,which have both a high active oxygen stability in the presence ofdetergent constituents and a controlled release, in particular delayedrelease of sodium percarbonate in the aqueous phase.

The invention also provides a process for the preparation of genericcoated particles, such as coated sodium percarbonate particles, whereinit is possible to obtain coated particles with a different dissolvingtime, the shell amount being kept constant.

The invention also provides the use off the coated peroxygen compounds,in particular coated sodium percarbonate particles, as a bleachingcomponent in detergents, bleaching compositions and cleaningcompositions, in particular those which require a delayed release of theactive oxygen (O_(a)) in the aqueous phase.

“Peroxygen compounds” in this Application are to be understood asmeaning those particulate substances which release active oxygen in theaqueous phase. Examples are percarbonates, perborates, persulfates,perphosphates, persilicates and solid peroxycarboxylic acids.

Among the particulate peroxygen compounds, sodium percarbonate currentlyoccupies a prominent position, and for this reason the followingstatements are substantially directed towards sodium percarbonate.

Sodium percarbonate (2Na₂CO₃.3H₂O₂) is used as the active oxygencomponent in detergents, bleaching compositions and cleaningcompositions. Because of the inadequate storage stability of sodiumpercarbonate in a warm-humid environment and in the presence of variouswashing and cleaning components, in particular silicatic builders,sodium percarbonate must be stabilized against the loss of active oxygen(O_(a)). An essential principle for the stabilization comprisessurrounding the sodium percarbonate particles with a single- ormultilayer shell, each shell layer comprising one or more inorganicand/or organic shell components.

Solid detergents such as are used for bleaching textiles in the home andin industry in many cases comprise an enzyme, in addition tosurface-active agents and inorganic and/or organic builders and ableaching agent, such as, in particular, sodium percarbonate. The use ofenzymes is scarcely dispensed with in universal detergents, since withtheir aid the removal of various protective constituents from textilescan be achieved quickly and gently, even at low temperatures. The use ofproteases for the removal of protein-containing soiling is particularlywidespread, but nevertheless other enzymes, such as lipases, amylases,cellulases and cutinases, to which in each case other specific tasks areassigned, are also increasingly being used.

In the case of enzyme-containing detergents, the good solubility of thesodium percarbonate often acts as a disadvantage, since highconcentrations of active oxygen, which can impair the action of a numberof enzymes, including in particular also that of proteases, are alreadyavailable in the wash liquor shortly after the start of the washingprocess. A sodium percarbonate with delayed release of the active oxygenhas accordingly been required for enzyme-containing systems.

According to GB 174,891, for the purpose of increasing the O_(a)stability active oxygen compounds, and these also include sodiumpercarbonate, are sprayed with a water-glass solution and dried.Water-glass, that is to say a mixture of alkali metal silicates, is alsoa shell component in comparison examples in the process according toDE-OS 26 22 610. A water-glass solution with a modulus (SiO₂ to Na₂O) of3.3 and a solids concentration of 27.5% is employed here. However, ithas been found that alkali metal silicates do not have a stabilizingaction in a sufficient amount even if a thick shell layer is applied tothe sodium percarbonate particles.

According to DE-OS 24 17 572 a better stabilization can be achievedusing mixed inorganic salts, such as a combination of sodium sulfate andsodium carbonate. According to DE-OS 26 22 610 a further improvement isachieved by additionally employing an alkali metal silicate as a thirdcomponent in the coating. The products described have proved to berapidly soluble.

According to U.S. Pat. No. 4,325,933 magnesium sulfate is also suitableas a shell component. As can be seen from WO 95/02555 and EP-A 0 623553, magnesium sulfate as the sole shell component did not yet meet thestability requirements imposed on sodium percarbonate at that time. Thecoating of the sodium percarbonate particles described in the last twodocuments mentioned accordingly comprises, in addition to magnesiumsulfate or a magnesium salt of a carboxylic acid, additionally an alkalimetal salt from the series consisting of alkali metal carbonates, alkalimetal bicarbonates and alkali metal sulfates, and as a third componentan alkali metal silicate, it being possible for the shell components tobe arranged in one or in several layers.

In the process according to WO 95/02555 a water-glass solution with amodulus of 3.5 and a high concentration, namely 37° Bé, was used for thepreparation of a separate alkali metal silicate layer. To prepare shelllayers which additionally comprised sodium carbonate in addition tosodium silicate, solutions in which the content of alkali metal silicatewas lower were used. No suggestion according to which the alkali metalsilicate concentration of the solution to be sprayed could have aninfluence on the dissolving time of the sodium percarbonate coated withthis can be seen either from this document or from the documents citedabove.

It follows from EP 0 623 553 A1 that the rate of solution of coatedsodium percarbonate particles decreases with an increasing amount ofsodium silicate—in the case of a shell layer of 1.5 wt. % sodiumsilicate the dissolving time was stated as 3.5 minutes, in the case of ashell layer of 12.5 wt. % sodium silicate and a thin magnesium sulfatelayer (1.5 wt. %) on top it was stated as 9.0 minutes. A water-glasssolution with 2% SiO₂ was used here for the preparation of the first,that is to say innermost, layer, but the modulus was not disclosed.

The doctrine of WO 97/19890 is that sodium percarbonate with a singleshell layer of substantially sodium sulfate has an adequate activeoxygen stability if the core material has been produced by fluidized bedspray granulation. The dense particle build-up indeed led to a somewhatlower rate of solution, but this was not sufficient, as has since beenfound, adequately to prevent deactivation of enzymes.

To reduce the deactivating action of bleaching agents with respect toenzymes, it was proposed in WO 96/23354 to compound a detergent suchthat under standard conditions more than 80 wt. % of the detergent butless than 70 wt. % of the sodium percarbonate dissolves. A coated sodiumpercarbonate, the coating being, for example, low-melting organicsubstances, or a sodium percarbonate prepared by fluidized bed spraygranulation, the rate of solution of which is lower than that of asodium percarbonate produced by conventional crystallization, isemployed. In practice, these systems proved to be not completelysatisfactory because of an inadequate delay in the release of O_(a)and/or other problems.

In the detergents according to WO 97/45524, which comprise asurface-active cationic ester and an alkalinity system, it is alsoimportant that the alkalinity system is released in a delayed manner inthe aqueous phase. The substances having an alkaline action are also tobe understood as meaning bleaching agents, such as sodium percarbonate.A coating with a material which itself has a low solubility in water, asa result of which a delayed release of the sodium percarbonate isrendered possible, is regarded as a means for reducing the dissolvingtime. In addition to organic shell components, alkali metal and alkalineearth metal sulfates are regarded as suitable shell components forlengthening the dissolving time in this document. As the inventors ofthe present Application have found, the dissolving time cannot bereduced in an effective manner by the sulfates mentioned as the soleshell component.

In WO 97/45524, a coating with sodium silicate with a modulus of SiO₂ toNa₂O in the range from 1.6:1 to 3.4:1, in particular 2.8:1, is regardedas the preferred coating for the purpose of delayed release of sodiumpercarbonate. The sodium silicate is used in the form of an aqueoussolution, and the sodium percarbonate coated therewith comprises 2 to 10wt. %, in particular 3 to 5 wt. % sodium silicate, based on the coatedsodium percarbonate. Instead of sodium silicate, magnesium silicate isalso regarded as a suitable shell component for delaying the release ofactive oxygen. Indications of the manner in which sodium silicate ormagnesium silicate is to be applied to sodium percarbonate cannot befound from this document. In particular, there is no indication of anexpedient concentration of the alkali metal silicate solution to be usedfor coating sodium percarbonate. As already stated in the introduction,sodium percarbonate must also have a sufficiently high active oxygenstability, and this is under no circumstances achieved by coating solelywith an alkali metal silicate.

EP 0 992 575 A1 also contains the doctrine of the possibility oflengthening the dissolving time of sodium percarbonate by alkali metalsilicate: In this, 0.5 to 30 wt. % of an alkali metal silicate with amodulus of greater than 3 and less than 5 is either mixed with sodiumpercarbonate or applied to this in the form of a shell layer. By way ofexample, the shell layer comprises 9 wt. % sodium silicate. To improvethe active oxygen stability, specific hydroxycarboxylic acids ordicarboxylic acids can additionally be arranged in a single or inseveral shell layers. Other known stabilizers from the series consistingof magnesium sulfate, sodium sulfate, sodium carbonate and sodiumbicarbonate can additionally be present in the coating. The dissolvingtime is in the range from about 2 minutes to 300 minutes, depending onthe composition of the coating. It is clear from the examples that byusing a water-glass solution with a modulus of less than 3 the rate ofsolution can be lowered only moderately. Indications of theconcentration in which the water-glass solution is to be employed inorder to obtain a coated sodium percarbonate with a sufficiently longdissolving time cannot be found from this document.

The dissolving time can indeed be lengthened by application of an alkalimetal silicate layer to sodium percarbonate if a large amount of alkalimetal silicate is used as the shell material. However, a disadvantage ofsodium percarbonate coated in this way is that at the high use amountsof alkali metal silicate required, the alkali metal silicate originatingfrom the coating is not dissolved satisfactorily in the wash liquor andthese “shells” can therefore precipitate on the laundry as greying. Suchundissolved constituents can also lead to undesirable deposits in thewashing machine.

The object of the present invention is to provide coated particulateperoxygen compounds which, in spite of only a thin shell layer, releasethe active oxygen in a delayed manner in water.

The object is, in particular, to provide improved coated sodiumpercarbonate particles which, with the lowest possible amount of alkalimetal silicate in the coating, lead to the highest possible delay in therelease of the sodium percarbonate in the aqueous phase.

According to another object, the coated particles, which, like sodiumpercarbonate particles, readily lose active oxygen in a humid-warmenvironment, should have a sufficiently high active oxygen stabilityduring storage in a silo and in the presence of detergent constituents,in addition to the delayed release.

According to another object of the invention, a process with whichparticles coated according to the invention, such as, in particular,sodium percarbonate particles, are rendered accessible in a simplemanner is to be provided.

According to another object it should be possible, by adjusting theprocess parameters during the coating of the sodium percarbonateparticles, for the dissolving time to be adjusted reliably with acertain “time window” without the amount of shell material employedbeing increased.

Another object is directed at providing coated particles of peroxygencompounds, in particular coated sodium percarbonate particles, whichrelease active oxygen in a relatively large amount in enzyme-containingdetergents only when the enzymes have fulfilled their task.

It has been found, surprisingly, that not only the modulus of awater-glass solution to be used for coating sodium percarbonate and theamount of alkali metal silicate in the coating are of importance for therate of solution of the coated sodium percarbonate, but also theconcentration of alkali metal silicate in the water-glass solution to beapplied and additionally the arrangement of at least two shellcomponents, of which one is primarily responsible for the active oxygenstability and the second is responsible for controlling the dissolvingtime, in at least two shell layers.

It has furthermore been found that by the choice of concentration ofalkali metal silicate in the water-glass solution to be used, thedissolving time can be varied widely for the same amount of alkali metalsilicate in the shell layer. At a fixed amount of alkali metal silicatein the coating, the dissolving time can be increased greatly if sodiumpercarbonate is coated using an aqueous alkali metal silicate solutionwhich has, instead of an alkali metal silicate concentration of, forexample, 20 wt. %, one of, for example, only 5 wt. %. Utilizing thissurprising effect, the abovementioned objects and further objects suchas can be seen from the further description and the examples can beachieved.

The invention provides coated particulate peroxygen compounds, inparticular coated sodium percarbonate particles, with a delayed releaseof the active oxygen in the aqueous phase, comprising at least two shelllayers on a core of the peroxygen compound, wherein an innermost layer,which makes up 2 to 20 wt. %, based on the coated particles, comprisesat least one hydrate-forming inorganic salt and an outer layer comprisesan alkali metal silicate with a modulus of SiO₂ to M₂O (M=alkali metal)of greater than 2.5, in particular greater than 3, characterized in thatthe outer layer comprises as the main component 0.2 to 3 wt. %, based onthe coated particles, of an alkali metal silicate and has been preparedusing an aqueous solution containing alkali metal silicate with aconcentration in the range from 2 to 20 wt. % alkali metal silicate.

The subclaims of the coated particles relate to preferred embodiments,and in particular to coated sodium percarbonate particles.

The coated sodium percarbonate particles according to the invention canhave a sodium percarbonate core which has been produced by any desiredpreparation process and can comprise stabilizers which are known per se,such as magnesium salts, silicates and phosphates. Preparation processeswhich are conventional in practice are, in particular, so-calledcrystallization processes, and fluidized bed spray granulationprocesses. In the crystallization processes, hydrogen peroxide andsodium carbonate are reacted in an aqueous phase to give sodiumpercarbonate and, after crystallization, the latter is separated offfrom the aqueous mother liquor. While in earlier processes sodiumpercarbonate was crystallized out in the presence of a relatively highconcentration of an inert salt, such as sodium chloride, processes havesince been disclosed in which the crystallization can also take place inthe absence of a salting-out agent—reference is made to EP-A 0 703 190by way of example.

In fluidized bed spray granulation for the preparation of sodiumpercarbonate, an aqueous hydrogen peroxide solution and an aqueous sodasolution are sprayed on to sodium percarbonate seeds, which are in afluidized bed, and at the same time water is evaporated. The granuleswhich grow in the fluidized bed are taken off from the fluidized bed intotal or with grading. The WO specification 95/06615 is referred to asan example of fluidized bed spray granulation.

Finally, sodium percarbonate which has been produced by a processcomprising bringing solid soda or a hydrate thereof into contact with anaqueous hydrogen peroxide solution and drying can also be the core ofparticles according to the invention.

In respect of a high internal stability of the sodium percarbonate corein the presence of detergent constituents, it is particularly expedientif the average particle diameter is greater than 0.5 mm, andparticularly preferably in the range from 0.5 to 1 mm. The particlespectrum expediently contains substantially no particles smaller than0.2 mm.

Preferably the fraction of particles with a diameter smaller than 0.4 mmis less than 10 wt. %, particularly preferably less than 5 wt. %.

The diameter of the sodium percarbonate particles which are coated withat least two layers is only slightly greater than that of the sodiumpercarbonate core. In general, the thickness of the total coating of thesodium percarbonate core is less than 20 μm. The layer thickness of thelayers, of which there are at least two, is preferably in the range from2 to 15 μm, in particular 4 to 10 μm. Since the amount of the innermostshell layer of the sodium percarbonate particles coated according to theinvention as a rule makes up a significantly greater proportion than theouter layer comprising alkali metal silicate, the thickness of theinnermost layer is also greater than that of the outer layer comprisingalkali metal silicate.

The term “outer shell layer comprising alkali metal silicate” meanseither the outermost shell layer of a coating comprising at least twolayers or a shell layer which in its turn can be covered by and cancover one or more layers.

Although in the following description individual layers are referred to,analogously to in the prior art, it should be noted that theconstituents of the layers lying on top of one another can pass into oneanother at least in the boundary region. This at least partialpenetration results from the fact the during coating of sodiumpercarbonate particles which have an innermost shell layer, this shelllayer is at least partly dissolved on the surface when a solution whichcontains a shell component(s) of a second shell layer is sprayed on.

The coating of the sodium percarbonate is carried out in a manner knownper se. In principle, the particles to be coated are brought intocontact once or several times, as uniformly as possible, with a solutioncontaining one or more shell components, and are dried at the same timeor subsequently. For example, the bringing into contact can be effectedon a granulating plate or in a mixer, such as a tumble mixer. Thecoating is particularly preferably carried out by fluidized bed coating,wherein firstly a first solution containing the shell component(s) forformation of an innermost layer and then a second solution containingthe shell component(s) for formation of an outer layer are sprayed on tothe sodium percarbonate or sodium percarbonate coated with one or morelayers, which is in a fluidized bed, and are dried at the same time withthe fluidized bed gas. The fluidized bed gas can be any desired gas, inparticular air, air heated directly with a combustion gas and with a CO₂content in the range from, for example, 0.1 to about 15%, pure CO₂,nitrogen and inert gases. Reference is made to the documentsacknowledged in the introduction for a detailed description of fluidizedbed coating.

The sodium percarbonate particles according to the invention comprise,in the innermost shell layer, at least one inorganic salt which iscapable of hydrate formation. In addition to this, the innermost shelllayer can also comprise other inorganic salts and/or organic compoundswhich have a stabilizing action, such as alkali metal salts ofcarboxylic acids or hydroxycarboxylic acids. The innermost shell layerparticularly preferably comprises one or more salts from the seriesconsisting of alkali metal sulfates, alkali metal carbonates, alkalimetal bicarbonates, alkali metal borates and alkali metal perborates.Although these salts can be both lithium salts, sodium salts andpotassium salts, the sodium salts are preferred.

According to an alternative embodiment, the innermost layer can alsocomprise magnesium sulfate, by itself or as a mixture with one or moreof the abovementioned salts.

According to a particularly preferred embodiment, the innermost shelllayer substantially comprises sodium sulfate, which can also be presentin part in the hydrated form. The term “substantially” is understood asmeaning that sodium bicarbonate or a double salt of sodium bicarbonate,such as sesquicarbonate or Wegscheider salt, can be contained at leastin the boundary layer between the sodium percarbonate core and theinnermost layer.

The innermost shell layer of coated sodium percarbonate particlesaccording to the invention in general makes up 2 to 20 wt. %, based onthe coated sodium percarbonate. The shell amount stated is the shell inthe hydrate-free form. The innermost shell layer preferably makes up 3to 10 wt. %, particularly preferably 4 to 8 wt. %, based on the coatedsodium percarbonate and calculated as the non-hydrated form. Since theinnermost shell layer comprises a hydratable inorganic salt, the shellamount can increase by storage in a damp atmosphere due to hydrateformation.

Sodium percarbonate particles coated according to the invention compriseone or more outer layers on the innermost layer. One of these outerlayers, preferably that which is arranged directly on the innermostshell layer, is the layer according to the invention comprising alkalimetal silicate. The module of the alkali metal silicate in the solutioncontaining alkali metal silicate used to build up this layer is greaterthan 2.5, and is preferably in the range from 3 to 5, and particularlypreferably in the range from 3.2 to 4.2. The modulus is the molar ratioof SiO₂ to M₂O, wherein M represents an alkali metal, and thusrepresents lithium, sodium or potassium or a mixture of alkali metals.Sodium silicate is preferred.

According to a particularly preferred embodiment of the invention, theouter layer comprising alkali metal silicate is a layer whichsubstantially comprises alkali metal silicate, sodium silicate beingparticularly preferred. The term “alkali metal silicate”, as can be seenfrom consideration of the modulus, is to be understood as meaning thatthis is to be understood as meaning all alkali metal silicates whichgive on average the modulus stated. The alkali metal silicate solutionto be used as the spray solution is preferably a so-called water-glasssolution, in particular a sodium water-glass solution.

If the innermost shell layer comprises constituents which have analkaline action, such as sodium carbonate, the modulus on an alkalimetal silicate layer on the innermost shell layer can become somewhatlower and therefore shorten the dissolving time, since interactionsbetween the constituents of the shell layers cannot be ruled out atleast in the boundary region.

For the formation of the shell layer comprising alkali metal silicate itis also possible to use a gas enriched in CO₂ or pure CO₂ as thefluidized bed gas or as the propellant gas for the spray solutioncontaining alkali metal silicate. By this means the pH of the alkalimetal silicate solution is lowered during the coating, as a result ofwhich the modulus and consequently the dissolving time of the coatedsodium percarbonate are increased.

According to a particularly preferred embodiment of the invention, theinnermost shell layer comprises substantially sodium sulfate and theouter layer adjacent thereto comprises substantially sodium silicate,the modulus of which is in the range from 3 to 5, preferably 3.2 to 4.2.Particularly preferably, the innermost shell layer comprises 2 to 10 wt.% sodium sulfate (calculated as the hydrate-free form) and the outerlayer comprises 0.3 to less than 1 wt. % sodium silicate with the abovementioned modulus, in each case based on the coated sodium percarbonate.

Although sodium percarbonate particles with at least two shell layers,one shell layer of which comprises sodium silicate or substantiallycomprises sodium silicate, are known in the prior art, the inventors ofthe present Application found for the first time that the sequence ofthe layer arrangement has a considerable influence on the rate ofsolution of the coated sodium percarbonate particles. It is thusessential in the process according to the invention that the layercomprising alkali metal silicate is not directly on the sodiumpercarbonate core, but is arranged as an outer layer, preferably as asecond layer. By the layer arrangement according to the invention,products which release sodium percarbonate in the aqueous phaseconsiderably more slowly than products with the reverse layer sequencesuch as are already known from the prior art can be obtained with thesame amount of alkali metal silicate and same modulus and the sameconcentration of the spray solution containing alkali metal silicate. Bythe arrangement according to the invention of the layers it is thuspossible for products with a long dissolving time already to be obtainedwith a very small amount of alkali metal silicate in the shell layer. Inthe prior art, a considerably higher amount of silicate was necessary toachieve the same dissolving time. By the smaller amount of alkali metalsilicate with a simultaneously long delay in the release of the sodiumpercarbonate, it has been possible to avoid the problem of greying oflaundry.

A further advantage which results from the low amount of silicate shellis that because of the very thin alkali metal silicate shell layer, onlya relatively small amount of dust comprising alkali metal silicate candevelop in the context of the fluidized bed coating. This small amountof dust can be introduced into the continuous process for thepreparation of sodium percarbonate by fluidized bed spray granulationwithout adversely changing the properties of the sodium percarbonate.

A water-glass solution of conventional quality can be used in theprocess according to the invention, that is to say no specificallypurified, for example iron-depleted, water-glass solution has to beused, because the shell layer comprising alkali metal silicate is notdirectly on the sodium percarbonate core and only little dust isobtained.

It is assumed that the layer sequence according to the invention is oneof the reasons why only a small amount of alkali metal silicate isnecessary. By application of the innermost layer a very much smoothersurface is evidently generated compared with the surface of the sodiumpercarbonate core, so that a closed effective shell layer can beproduced with a small amount of alkali metal silicate.

A further feature of the coated sodium percarbonate particles which isessential to the invention is that an aqueous solution containing alkalimetal silicate with a concentration in the range from 2 to 20 wt. %,preferably 3 to 15 wt. % and particularly preferably 5 to 10 wt. % ofalkali metal silicate is used for the preparation of the outer shelllayer comprising alkali metal silicate. According to a particularlypreferred embodiment, the coated sodium percarbonate particles accordingto the invention are prepared using a sodium water-glass solution with aconcentration of 2 to 20 wt. %, in particular 5 to 10 wt. %, and amodulus in the range from 3 to 5, and preferably 3.2 to 4.2.

Finally, it has also been found that the rate of spraying, that is tosay the spraying time for application of a predetermined amount ofalkali metal silicate, has an influence on the dissolving time: Byincreasing the spraying time it is possible to increase the dissolvingtime.

The coated sodium percarbonate particles comprise, in an outer layer,0.2 to 3 wt. % alkali metal silicate with a modulus of greater than 2.5,and preferably greater than 3. A further lowering of the amount ofalkali metal silicate is possible in principle, but the effect ofincreasing the dissolving time is then only moderate. In the same way,an increase above 3 wt. % alkali metal silicate, for example >3 to 5 wt.%, is possible if a particularly long dissolving time is desired forparticular use purposes.

According to A preferred embodiment, the coated sodium percarbonateparticles comprise 0.2 to 1 wt. %, and preferably 0.3 to less than 1 wt.% alkali metal silicate, preferably sodium silicate, in an outer shelllayer. Such a product is particularly suitable for use inenzyme-containing solid detergents. In spite of the only small layerthickness of the outer layer comprising alkali metal silicate, there isa very effective lengthening of the dissolving time and thereforedelayed release of sodium percarbonate. In the case of, for example, anaverage particle diameter of 0.8 mm and a sodium silicate layer of 0.5to 1 wt. %, the layer thickness is equal to or less than 1 μm.

Particularly preferred coated sodium percarbonate particles, such as, inparticular, those which comprise sodium sulfate as the innermost shelllayer and 0.3 to less than 1 wt. % sodium silicate as the outer shelllayer, have a dissolving time of more than 5 minutes, in particular morethan 10 minutes. Dissolving time here means that time which isdetermined by conductometric monitoring for 95% dissolution in water at15° C. at a concentration of 2 g/l.

In addition to the innermost shell layer and an outer shell layercomprising sodium silicate, it may be expedient if the coated particleshave one or more further shell layers, which can be closed ornon-closed, on the outer layer comprising alkali metal silicate, whichis preferably a pure sodium silicate layer.

According to a preferred embodiment, the shell component of an outermostshell layer is a finely divided inorganic or organic free-flowingauxiliary substance which completely or partly covers the surface of theparticles. The risk of caking of sodium percarbonate particles whichhave a layer of substantially alkali metal silicate on an innermostshell layer is avoided by the presence of a free-flowing auxiliarysubstance. Particularly suitable free-flowing auxiliary substances arefinely divided inorganic compounds from the series consisting of oxides,mixed oxides and silicates; these substances can be of natural orsynthetic origin.

Nanoscale substances, such as precipitated and pyrogenic silicas,aluminium oxide and titanium dioxide, which can be either hydrophilic orhydrophobic, are particularly suitable. Among the silicatic substances,pyrogenically prepared aluminium silicate and montmorillonite arementioned by way of example. Such substances have a BET surface area ofpreferably 20 to 500 m²/g, so that only a very small amount used of suchsubstances is sufficient to form an effective shell layer.

The preparation of the coated particles, in particular the coated sodiumpercarbonate particles, comprises coating processes which are known perse, preferably fluidized bed coating, at least two shell layers beingformed. The process is characterized in that for the preparation of anouter shell layer comprising alkali metal silicate as the maincomponent, an aqueous solution containing alkali metal silicate with analkali metal silicate concentration in the range from 2 to 20 wt. % anda modulus of SiO₂ to M₂O (M=alkali metal) of greater than 2.5 is usedand this solution is sprayed on to sodium percarbonate particles whichhave at least one innermost shell layer of at least one hydrate-formingshell component in a fluidized bed, with simultaneous evaporation ofwater, until the outer layer comprises 0.2 to 3 wt. % alkali metalsilicate.

According to a preferred embodiment, an alkali metal silicate solutionwith a modulus in the range from 3 to 5 with an alkali metal silicatecontent in the range from 2 to 15 wt. %, and in particular 5 to 10 wt.%, is used to form the shell layer comprising alkali metal silicate.Preferably, such a solution, which is here in particular a sodiumwater-glass solution, is sprayed on to sodium percarbonate particlescomprising at least one innermost shell layer in an amount such that theouter shell layer comprises 0.3 to 2 wt. %, preferably 0.3 to less than1 wt. % alkali metal silicate, in particular sodium silicate.

So that the capacity of a unit for fluidized bed coating is not reducedtoo much by the use of the dilute alkali metal silicate solutions, it ispossible to keep the spraying time constant by increasing thetemperature of the fluidized bed gas and/or the flow rate thereof.Nevertheless, the increase in dissolving time may not be optimum due tothis measure.

According to one embodiment, a closed or non-closed shell layer can beapplied to the outer shell comprising alkali metal silicate as the maincomponent by conventional fluidized bed coating.

According to an alternative and preferred embodiment, a free-flowingauxiliary substance can be applied to sodium percarbonate particlescoated with at least two layers by bringing these into contact with thevery finely divided free-flowing auxiliary substances. The amount offree-flowing auxiliary substance employed is preferably significantlybelow 1 wt. %, and particularly preferably below 0.5 wt. %. For example,it is possible to bring the coated sodium percarbonate which has beentaken off from the coating unit into contact with the pulverulentfree-flowing auxiliary substance in a fall pipe or a pipe for pneumaticconveying or in a mixer, the auxiliary substance being adsorbed on tothe surface of the coated sodium percarbonate particles.

By the process according to the invention it is possible for coatedsodium percarbonate particles which release sodium percarbonate andtherefore active oxygen in the aqueous phase in a controlled manner tobe obtained in a reliable manner. The dissolving time of the coatedsodium percarbonate can thus be matched in a targeted manner to the userequirements of an enzyme-containing detergent.

The invention also provides the use of the particles according to theinvention, in particular the coated sodium percarbonate particles, as ableaching agent in detergents, bleaching compositions and cleaningcompositions. The detergents, bleaching compositions and cleaningcompositions are, in particular, those which comprise at least oneenzyme. Such compositions expediently comprise 5 to 50 wt. %, preferably10 to 40 wt. %, and in particular 15 to 25 wt. % of the sodiumpercarbonate coated according to the invention. The particles having ableaching action which have been coated according to the invention canbe employed in detergents, bleaching compositions and cleaningcompositions of any desired composition. Such compositions comprise asthe main components, in addition to the bleaching component:

-   -   Surface-active agents from the series consisting of cationic,        anionic, nonionic, amphoteric and ampholytic surface-active        agents.    -   Inorganic and/or organic builders, the main action of which        comprises sequestering or complexing of the metal ions        responsible for hardness of water. Examples are: zeolites,        laminar silicates, polyphosphates, aminopolyacetic acids,        aminopolyphosphonic acids and polyoxycarboxylic acids.    -   Components having an alkaline action, such as alkanolamines;        inorganic electrolytes, such as silicates, carbonates and        sulfates.    -   Bleaching activators from the series consisting of N-acyl        compounds and O-acyl compounds, such as        tetraacetylethylenediamine (TAED) and        nonanoyloxybenzenesulfonate (NOBS).    -   Enzymes, such as, in particular, lipases, cutinases, amylases,        neutral and alkaline proteases, esterases, cellulases,        pectinases, lactases and peroxidases.    -   Further constituents of the compositions can be stabilizers for        peroxides, such as, in particular, magnesium salts,        antiredeposition agents, optical brighteners, foam inhibitors,        disinfectants, corrosion inhibitors, fragrances, dyestuffs and        agents for regulating the pH.

The invention is illustrated further with the aid of the followingexamples. The experiments show the completely unexpected effect of theuse concentration of the sodium water-glass solution for the formationof the outer shell layer, the similarly unexpectedly high effect due toa very thin sodium silicate layer, and the influence of the modulus andof the layer sequence.

EXAMPLES General Instructions

Unless stated otherwise, sodium percarbonate with an average particlediameter of 750 μm and a fine particle content (smaller than 200 μm) ofsubstantially 0% is coated with a first shell layer of substantiallysodium sulfate in a fluidized bed in accordance with WO 95/19890. Ineach case 1,000 g sodium percarbonate, which has a shell layer of 6 wt.% sodium sulfate, based on the coated product and calculated as thehydrate-free form, were coated. The product coated in this way wascoated with a water-glass solution in a fluidized bed coating unit(Strea 1—Aeromatic), which resulted in a second shell layer. Sprayingwas carried out at a fluidized bed temperature of about 60° C. Airserved as the fluidized bed gas at an intake temperature in the regionof about 100° C. After the spraying the feed air temperature was loweredsomewhat and after drying was carried out at a fluidized bed temperatureof 75° C.

The amounts employed, the modulus and the concentrations of sodiumwater-glass, as well as the dissolving times in minutes (2 g ofproduct/l of water, 15° C., 95% dissolution determinationconductometrically) can be seen from the following tables.

Examples 1 to 3

A sodium water-glass solution (Na-WG) diluted with water and with amodulus of 3.35 was employed for the coating. The concentration of thesolution to be sprayed was varied. A commercially available Nawater-glass solution with a solids content of 36 wt. % was used toprepare the spray solutions. The sodium percarbonate coated with onelayer was in each case coated with 0.75 wt. % sodium silicate (modulus3.35).

The spraying time in examples 1 to 3 was in each case about 20 minutes.The dissolving time as a function of the concentration of the spraysolution follows from table 1. It is found that the dissolving timeincreases markedly with a decreasing Na-WG concentration in the spraysolution, that is to say sodium percarbonate is released from the coatedproduct in the aqueous phase in an increasingly delayed manner. TABLE 1Dissolving Example no. Na-WG concentration (wt. %) time (min) 1 20 8.0 210 14.8 3 5 19.6

Examples 4 to 8

In a first stage, sodium percarbonate with a particle spectrum ofgreater than 0.4 mm was coated with sodium sulfate in a shell amount inthe range from 3 to 6 wt. %. The product coated in this way was in eachcase coated in a second stage using a 10 wt. % sodium water-glasssolution, for the preparation of which a commercially available Na-WGsolution (different origin to that in examples 1 to 3) with a modulus of3.34 and a solids concentration of 35.6 wt. % was employed. The amountof sodium silicate in the shell layer was in each case 0.75 wt. %. Theresults follow from table 2. TABLE 2 1st layer Shell amount 2nd layerDissolving Example no. wt. % Na₂SO₄ Shell amount wt. % Na-WG time (min) 4* 6 0 1.3 5 6 0.75 11.0 6 5 0.75 11.0 7 4 0.75 13.3 8 3 0.75 14.4*not according to the invention

Examples 9 and 10

Sodium percarbonate coated with 6 wt. % Na₂SO₄ (innermost layer) wascoated with 1.5 and 3.0 wt. % sodium silicate respectively. Acommercially available sodium water-glass solution diluted to a solidscontent of 10 wt. % and with a modulus of 3.34 and a concentration of35.6 wt. % was employed. The results follow in table 3. TABLE 3Dissolving Example no. Na-WG shell amount (wt. %) time (min) 9 1.5 35 103.0 80

Examples 11 and 12

Sodium percarbonate was first coated with 0.75 wt. % sodium silicate(1st layer) from a water-glass solution with a modulus of 3.4, and thencoated with 6 wt. % sodium sulfate (2nd layer). The sodium silicatelayer was produced using a spray solution with 10 wt. % sodium silicate(modulus 3.4). The layer sequence of example E 11 is not according tothe invention.

The sodium percarbonate of example E 12 according to the inventioncoated with two layers was produced employing the same spray solutionsand the same sodium percarbonate, but the layer sequence was thereverse, that is to say according to the invention. Table 4 shows theresults. The dissolving time of the example which is not according tothe invention is considerably shorter than that of the example accordingto the invention. TABLE 4 Dissolving Example no. Sequence of the layerstime (min) 11 1st Na-WG; 2nd Na₂SO₄ 4.1 12 1st Na₂SO₄; 2nd Na-WG 11.0

Example 13

Sodium percarbonate coated with 6 wt. % Na₂SO₄ (corresponding to example4) was sprayed in a fluidized bed with a 10 wt. % Na water-glasssolution, prepared from commercially available Na water-glass with amodulus of 4.1 and a concentration of 28.5 wt. %, to form a secondlayer. The shell amount of the 2nd layer was 0.75 wt. % sodium silicate.

The dissolving time of the product of example 13 was 21 minutes. Thedissolving time of the product prepared analogously but using an Nawater-glass solution with a modulus of 3.34 (=example 5) was 11 minutes.The dissolving time thus increases as the modulus increases.

Examples 14 and 15

Commercially available sodium percarbonate coated with 6 wt. % Na₂SO₄(Q35 from Degussa) was coated using a 5 wt. % sodium water-glasssolution, prepared from a commercially available Na-WG solution with amodulus of 3.2 and a solids (Na₂O+SiO₂) concentration of 32.9 wt. %. Theshell amount and dissolving times follow from table 5. TABLE 5Dissolving Example no. Na-WG shell amount (wt. %) time (min) 14 0.7521.5 15 0.50 14.5

Examples 16 to 18

Commercially available sodium percarbonate coated with 6 wt. % Na₂SO₄(quality 30 and 35 from the Applicant) was coated in a pilot plant onthe 150 kg scale using a 10 wt. % sodium water-glass solution with amodulus of 3.2. Coating was carried out analogously to the process ofU.S. Pat. No. 6,239,095. The shell amount of sodium silicate, theparticle spectrum and the dissolving times follow from table 6. TABLE 6Shell Dissolving Example amount time D₅₀ D₁₀ D₉₀ no. Quality (wt. %)(min) (mm) (mm) (mm) 16 Q 30 0.75 13.0 0.55 0.35 0.90 17 Q 35 0.50 14.50.87 0.55 1.25 18 Q 35 0.75 21.5 0.78 0.50 1.20

The examples according to the invention are also distinguished by adelayed release of the active oxygen (dissolving time) due to a highactive oxygen stability during storage substantially determined by theinnermost layer.

Table 7 shows the storage stability, in a zeolite-containing heavy-dutydetergent, of the products of examples 17 and 18 coated with two layersand of the Q35 employed—stored in E2 detergent packs at 35° C., 80% rel.atmospheric humidity. An unexpectedly high increase in stability isobtained by the second layer of sodium silicate, in spite of the smallamount employed and therefore the low layer thickness. The differencesin the rel. residual O_(a) of examples E17 and E18 lie within the rangeof variation of the test, and the two products therefore have about thesame stability. TABLE 7 Relative residual O_(a) TAM value 2nd layer ofNa (%) (μw/g) Example no. silicate (wt. %) after 4 weeks after 8 weeks24 h/60° C. Q35 0 92 69 23 17 0.50 95 84 11 18 0.75 96 82 11

The TAM values (TAM=thermal activity monitor) show that by theapplication of the very thin sodium silicate layer to an NaPc coatedwith sodium sulfate the TAM value decreases very markedly in anunforeseeable manner. The internal stability of the coated particles istherefore increased significantly.

1-18. (canceled)
 19. Coated peroxygen particles having a delayed releaseof active oxygen into an aqueous phase, each particle comprising a core,an innermost shell layer and an outer shell layer surrounding said core,wherein: a) said core comprises said peroxygen compound; b) saidinnermost shell layer makes up 2-20 wt % of said coated particle andcomprises at least one hydrate-forming inorganic salt; c) said outershell layer comprises an alkali metal silicate present at 0.2 to 3 wt %of said coated particle and with a modulus of SiO₂ to M₂O of greaterthan 2.5, wherein M is an alkali metal, and wherein said outer layer hasbeen prepared using an aqueous solution comprising 2-20 wt % alkalimetal silicate.
 20. The coated particles of claim 19, wherein saidaqueous solution used to prepare said outer shell layer comprises amodulus of SiO₂ to M₂O in the range of from 3 to 5 and a concentrationof alkali metal silicate in the range of from 3 to 15 wt %.
 21. Thecoated particles of claim 19, wherein said aqueous solution used toprepare said outer shell layer comprises 2 to 20 wt % sodium silicate.22. The coated particles of claim 19, wherein said alkali metal silicatein said outer shell layer comprises 0.3 to less than 1 wt % of saidcoated particle, and the time needed to dissolve 95% of said coatedparticles in water at 15° C. and a concentration of 2 g/l is longer than5 minutes.
 23. The coated particles of claim 19, wherein said innermostshell layer comprises one or more salts from the group consisting of:alkali metal sulfates; alkali metal carbonates; alkali metalbicarbonates; alkali metal borates; and alkali metal perborates.
 24. Thecoated particles of claim 19, wherein said innermost shell layerconsists essentially of sodium sulfate and said outer shell layer on topof said innermost shell layer consists essentially of sodium silicateswith a modulus in the range from 3 to
 5. 25. The coated particles ofclaim 24, wherein said innermost shell layer comprises 2 to 10 wt %sodium sulfate and said outer shell layer comprises 0.3 to less than 1wt % sodium silicates, in each case based on the toal weight of saidcoated particle.
 26. The coated particles of claim 19, wherein eachparticle comprises one or more additional shell layers on said outershell layer.
 27. The coated particles of claim 26, wherein each particlecomprises an outermost layer of a finely divided inorganic or organicfree-flowing auxiliary substance.
 28. The coated particles of claim 19,wherein the average particle diameter is in the range from 0.5 to 1 mmwith substantially no particles smaller than 0.2 mm.
 29. The coatedparticles of claim 28, wherein said particles have a D₁₀ value of atleast 0.35 mm.
 30. The coated particles of claim 28, wherein thefraction of particles with a diameter smaller than 0.4 mm is less than10 wt %.
 31. The coated particles of claim 19, wherein said peroxygencompound is sodium percarbonate.
 32. A process for the preparation ofthe coated peroxygen particles of claim 31, comprising: a) spraying saidaqueous solution comprising 2-20% alkali metal silicate onto sodiumpercarbonate particles comprising said core and said innermost shelllayer; b) simultaneously or subsequently evaporating water from theparticles sprayed in step a) to form said outer shell layer.
 33. Theprocess of claim 32, wherein said alkali metal silicate solution is asodium water-glass solution.
 34. The process of claim 32 wherein: a)said innermost layer is applied to said core, wherein said corecomprises said sodium percarbonate and said innermost layer comprises 3to 10 wt % of sodium sulfate, calculated as the hydrate-free form andbased on the coated sodium percarbonate particle; and b) a sodiumwater-glass solution substantially comprising sodium silicate with amodulus in the range from 3 to 5 and with a concentration of sodiumsilicate in the range from 5 to 10 wt % is applied to said sodiumpercarbonate particles by spraying, said spraying being ended afterapplication of 0.2 to 3 wt % sodium silicate.
 35. A process for thepreparation of the coated peroxygen particles of claim 31, comprising:applying said outer layer by fluidized bed coating particles having atleast one innermost shell layer.
 36. The process according to claim 32,wherein sodium percarbonate coated with an innermost layer of at leastone hydratable salt and an outer layer of alkali metal silicates isbrought into contact with a pulverulent inorganic free-flowing auxiliarysubstance in an effective amount.
 37. The coated particle of claim 27,wherein said free-flowing auxiliary substance is selected from the groupconsisting of: precipitated silica; pyrogenic silica; aluminium oxide;titanium dioxide; aluminium silicate; and montmorillonite.
 38. Adetergent composition with a delayed release of active oxygen into anaqueous phase, comprising the coated sodium percarbonate particles ofclaim
 31. 39. The detergent composition of claim 38, wherein said coatedsodium percarbonate particles comprise 5 to 50 wt % of the composition.